1. Field of the Invention
Application of this invention would be useful in manned and unmanned airships and balloons or other buoyant and semi-buoyant vehicles, and relates to the reversible adjustment of aerostatic lift via pneumatic means without the use of offsetting ballast.
2. Description of the Related Art
The ability to economically adjust aerostatic lift has long been a goal of lighter-than-air vehicle designers. It is especially useful in asymmetric cargo operations where payloads may be exchanged without the use of offsetting ballast. Operations such as transport of materiel from military bases into a combat theater of operations or from pre-positioned naval ships to land based assembly areas necessitate asymmetric capabilities. Delivery of humanitarian disaster relief supplies and the application of water, slurry, foam, or fog for aerial fire suppression operations also require asymmetric capabilities. In sport ballooning, small changes in lift allow maneuver to different altitudes to facilitate exploitation of favorable winds. In hot air balloons this is achieved through variable input of heat, however in gas balloons, it has largely been limited to the venting of lifting gas or the release of ballast. With the current invention, such adjustments could be made continuously without depletion of ballast. Similar needs may face the emerging market of high altitude aerial telecommunications and surveillance platforms. With available solar energy to power the current invention, such altitude adjustments could be made indefinitely.
Control of buoyancy in lighter-than-air flight has been a subject explored extensively since the first flights of the montgolfiere and charliere balloons in 1783. In both the early montgolfieres and modern hot air balloons buoyancy control is achieved through variable input of heat. This process alters the density of air inside the balloon and thus affects the balloon's lift. After first conducting trials with ground-based fires, later techniques used in-flight fires of straw and other items placed in a small onboard wire basket. The method was difficult to control and provided limited heat, but effectively demonstrated the potential of hot air balloons. It was not until 1960 that Ed Yost ushered in the era of modern hot air ballooning with the use of a propane burner, providing much greater energy density and controllability. In charlieres or gas balloons, lift is provided by the lower molecular weight and density of the lifting gas, such as hydrogen or helium. In these systems buoyancy control has largely been limited to the venting of lifting gas and the release of ballast. With relatively cheap hydrogen or coal gas used in the 1800s, this method was practical. An effort to combine the two aerostatic balloon systems of hot air and gas was undertaken by Jean Francois Pilâtre de Rosier, himself the first aeronaut (along with the Marquis D'Arlandes), who in 1785 built what became known as the rosiere balloon. While his flight ended tragically with the vehicle catching fire and Pilâtre falling to his death, it was a modern rosiere balloon, the Breitling Orbiter III, using helium and a propane burner system that finally completed a round the world balloon flight in 1999.
Interestingly, on Dec. 3, 1783, the same year of the first manned balloon flights, a French military officer and aeronautical theorist, Jean-Baptiste-Marie-Charles Meusnier de la Place proposed the first elongated ellipsoidal balloon for the purpose of making it steerable, or dirigible. His design was presented to the French Academy of Sciences, and included the use of an envelope divided by an ellipsoidal hemispheric diaphragm, which was called a ballonet. It was proposed that the upper portion of the divided envelope could be filled with lifting gas, (at the time hydrogen) and the lower portion could be variably filled with air from the surrounding atmosphere through the use of an air pump. Ostensibly this was to serve two purposes. The first was to maintain the streamlined shape of the airship. As the airship rose in altitude, the lifting gas would expand. As it did, the pressure from the lifting gas would force air to escape from the air filled portion and the streamlined shape would remain taught without bursting. As the airship descended, the lifting gas would contract. In order to keep the envelope of the airship from becoming flaccid and bending or deforming, air would be pumped in to the lower portion to maintain pressure and shape. The second purpose Meusnier proposed was that the method might be used to deliberately control buoyancy. Muesnier's design was never built, partly due to his early death nine years later, but also due to technical challenges. The availability of air pumps with high flow rates, sufficient pressure, and of lightweight construction would not occur for decades and the tensile strength and impermeability of fabric of the time was insufficient for sustaining pressure differentials necessary for significant buoyancy control. 68 years would pass before the first successful airship was flown, but since his initial design, all successful non-rigid and semi-rigid airships have incorporated some form of ballonet to maintain a streamlined shape. The only significant modifications have been a reduction in scale of the ballonet and the combined use of both fore and aft ballonets to allow for trim adjustment (pitching the nose up or down), which would then impart aerodynamic forces to adjust altitude, but the ballonet would not serve as an effective direct lift control system for other than minor adjustments. In airships, as in charliere gas balloons, aerostatic buoyancy control was to be accomplished through release of ballast and venting of gas.
Rigid airship manufacturers and operators, including Luftsciffbau Zeppelin Gmbh of Germany, adopted these same buoyancy control methods. Their airships, which became known as zeppelins, controlled lift primarily through the use of conventional aerostatic means. Hydrogen was vented through valves on the top of the airship, reducing lift, and ballast water was released to increase lift. Additionally, the airship could be flown with the nose pitched up or down by using aerodynamic elevators, creating positive or negative aerodynamic lift, but in so doing inducing significant drag, thus reducing the efficiency of the airship. As the shape of the airship was maintained by its rigid structure, there was no obvious need for the ballonet.
The discovery of helium, a nonflammable gas with perceived safety advantages first identified on Earth in 1895, led to its use in 1921 by the United States Navy in the pressure airship C-7. It became immediately apparent that the practice of venting helium would be quite expensive and other techniques were required for economical operation. As the Navy embraced helium for its rigid airships beginning with the Shenandoah, first flown in 1923, they incorporated an exhaust gas water recovery system to help offset the consumption of fuel and resulting decrease in weight during a flight. Experience with this ship lead to design innovations in the later airships Akron and Macon, including an improved exhaust gas water recovery system facilitated by the placement of the engines within the hull. While these methods were sufficient for replacing the weight of fuel consumed in flight, it could not be employed for significant asymmetrical cargo operations.
Other proposed prior methods have included the direct compression of either the lifting gas or air into small high-pressure storage containers. It has generally been found that such pressurization requires heavier and more energy intensive compressors, heavy storage containers, and often the use of gas cooling and heating systems to remove or add heat to the gases undergoing anisothermal volumetric change. Because the current invention requires applying only relatively small changes in pressure upon a larger volume, the required materials add less weight and the system uses less power. Another proposed prior method involves the intake and expulsion of water for use as ballast. Such a system is complex, expensive, heavy, and susceptible to fouling, and has many practical limitations including the availability of water at cargo destinations. A third proposed prior method has been the combination of aerodynamic lift with a lighter-than-air vehicle. Rather than merely operating a symmetrical airship with the nose pitched up as before, such designs incorporate a lifting-body geometry. Such hybrid designs have been proposed specifically to handle the asymmetric lift problem, however they introduce more problems than they solve. Namely, the hybrid suffers induced drag that results from aerodynamic lift and requires forward momentum to become airborne. The significant decrease in efficiency due to induced drag alone makes the hybrid vehicle approach economically less attractive.